Locking structure to high temperature
Because of atomic diffusion, metal alloys with nanometer-sized crystal grains do not retain their structure at high temperature. Xu et al. found that a minimum-interface structure allows a supersaturated aluminum-magnesium alloy to be retained at temperatures higher than the melting point. This system is known for high atomic diffusivity, highlighting the importance of the underlying interface structure. These observations have implications for designing structural alloys for high-temperature applications.
Science, abh0700, this issue p. 683
Abstract
High atomic diffusivity in metals enables substantial tuneability of their structure and properties by tailoring the diffusional processes, but this causes their customized properties to be unstable at elevated temperatures. Eliminating diffusive interfaces by fabricating single crystals or heavily alloying helps to address this issue but does not inhibit atomic diffusion at high homologous temperatures. We discovered that the Schwarz crystal structure was effective at suppressing atomic diffusion in a supersaturated aluminum–magnesium alloy with extremely fine grains. By forming these stable structures, diffusion-controlled intermetallic precipitation from the nanosized grains and their coarsening were inhibited up to the equilibrium melting temperature, around which the apparent across-boundary diffusivity was reduced by about seven orders of magnitude. Developing advanced engineering alloys using the Schwarz crystal structure may lead to useful properties for high-temperature applications.